The present invention relates to waste water treatment method and waste water treatment apparatus.
Organofluoric compounds and organochlorine compounds are chemically stable substances. The organofluoric compounds in particular are used for application such as surface-active agents since they have excellent properties in terms of heat resistance and chemical resistance.
However, it is difficult to microbially decomposite the organofluoric compounds or organochlorine compounds because they are chemically stable. Perfluorooctane sulfonic acid (PFOS) or perfluoro octanoic acid (PFOA), which is an example of the organofluoric compounds, is hardly decomposed in the ecosystem. This causes concern about harmful influence on the ecosystem. Thermal decomposition of PFOS or PFOA requires temperature as high as approx. 1000° C. since PFOS and PFOA are chemically stable. On the other hand, however, it is extremely difficult to decompose PFOS or PFOA in such a conventional treatment as to use microorganisms, photocatalysts or the like.
JP 2004-121962A discloses a conventional method and apparatus for using nanometer bubbles. In the method and apparatus for using nano bubbles, there have been utilized characteristics of nano bubbles such as an effect of surface activity or an effect of sterilization caused by decrease in buoyancy, increase in surface areas, intensification of surface activity, generation of a local high pressure field, and electrostatic polarization which appear in the nano bubbles. More specifically, it has been disclosed that mutual association of these characteristics makes it possible to lead to the adsorbing function of pollution components, the high speed cleaning function and the sterilization function of object surfaces, and thereby objects and/or waste-water are effectively cleaned under a low environmental load.
Also, JP 2003-334548A discloses a method for producing nano air-bubbles. The method for producing nano air-bubbles is composed of (i) a process for decomposing a part of liquid into gas in the liquid and (ii) a process for applying ultrasonic waves in the liquid, or (iii) a process for decomposing a part of liquid into gas and a process for applying ultrasonic waves.
Further, JP 2004-321959A discloses a waste liquid treatment apparatus. In the waste liquid treatment apparatus, ozone gas generated by an ozonizer and waste liquid drawn from the bottom of a treatment tank are fed to a micro bubble generator through a pressurization pump. The generated ozone micro bubbles are fed from openings of a gas blowout pipe into the waste liquid in the treatment tank.
However, the aforementioned JP 2004-121962A, JP 2003-334548A and JP 2004-321959A have following problems:    (1) It has not been disclosed that after micro-nano bubbles are added to treatment-receiving-water, the treatment-receiving-water containing micro-nano bubbles is introduced so that microorganisms are more activated. The term “micro-nano bubbles” herein refers to bubbles including both micro bubbles with a diameter of not more than 50 μm and not less than 1 μm and nano bubbles with a diameter of not more than 1 μm.    (2) It has not been disclosed that it is more effective in activating microorganisms than the case (1) that after micro-nano bubbles are added to treatment-receiving-water, the treatment-receiving-water and sludge containing microorganisms are mixed and introduced into a microbe tank.    (3) It has not been disclosed that after micro-nano bubbles are added to waste water containing organofluoric compounds or waste water containing organochlorine compounds, a first-stage microbial treatment is conducted, and then, after micro-nano bubbles are further added to the treatment-receiving-water, a second-stage microbial treatment is conducted to decomposite the above compounds.
As is stated above, there has not conventionally been known a method for decomposing the organofluoric compounds and the organochlorine compounds, which are chemically stable substances, reasonably at low costs.